The invention relates to a process for the production of citric acid which comprises subjecting a carbohydrate-containing material to a submerged fermentation with a citric acid producing strain of Aspergillus niger in the presence of metals such as iron and copper.
It is known that trace amounts of various metals such as iron, copper and zinc have a vital effect on the physiology of the organism used in the fermentation process. The metals not only promote the growth of the organism, they also have an effect on the yield of citric acid obtained from the carbohydrate-containing material used. It is known that although iron is required for the growth of microorganisms including Aspergillus niger, the presence of this metal can have a very detrimental effect on the citric acid yield obtained if this metal is present in the fermentation medium in larger than trace amounts. Various attempts have been made to remove surplus amounts of this metal e.g. by ion exchange, precipitation or complexation processes, also when using carbohydrate-containing materials which contain relatively small amounts of this metal. It has also been found that copper or morpholine can be used to counteract the detrimental effects of surplus amounts of iron.
It is an object of the invention to provide a process in which control of the trace metal content can be achieved in an economic and convenient manner.